The present invention relates to a clutch that transmits rotational driving force from a drive shaft to a driven shaft and does not transmit rotational force from the driven shaft to the drive shaft, and to a motor equipped with such a clutch.
In general, a motor used as a drive source for a power window apparatus or the like includes a rotary shaft, which is driven to rotate, and a speed reducing mechanism coupled to the rotary shaft via a clutch. The clutch operates to transmit rotational driving force from the rotary shaft to a worm shaft of the speed reducing mechanism and not to transmit rotational force from the worm shaft to the rotary shaft.
For example, Japanese Laid-Open Patent Publication No. 2002-39223 discloses a motor with a clutch having an annular clutch housing. The clutch housing accommodates a driving-side rotor, which rotates integrally with the rotary shaft, a driven-side rotor, which rotates integrally with the worm shaft, and rolling elements. The driven-side rotor includes a shaft portion and engaging projections extending radially outward from the shaft portion. A control surface is formed on the radially outer end face of each engaging projection. The distance between the control surface and the clutch housing varies along the rotational direction. The rolling elements are each located between the clutch housing and one of the control surfaces. When the driving-side rotor is driven to rotate by the rotary shaft, the driving-side rotor is engaged with the engaging projections of the driven-side rotor with respect to the circumferential direction. Accordingly, the rotational driving force from the rotary shaft is transmitted to the worm shaft via the driving-side rotor and the driven-side rotor. On the other hand, when the rotary shaft is not driven to rotate, the rolling elements are held between the control surfaces of the engaging projections and the clutch housing, thereby inhibiting rotation of the driven-side rotor. Rotational force of the worm shaft is thus not transmitted to the rotary shaft.
According to the clutch disclosed in Japanese Laid-Open Patent Publication No. 2002-39223, the engaging projections project radially outward from the shaft portion, and are engaged with the driving-side rotor when the rotary shaft is driven to rotate. When the rotary shaft is not driven to rotate, the engaging projections hold, together with the clutch housing, the rolling elements. However, the engaging projections, which project radially outward, increase the radial size of the clutch.